Poly(N-isopropylacrylamide) is a thermoresponsive polymer extensively studied for numerous applications in areas such as drug delivery, sensor technologies, and remediation. We are interested in designing a fluorescence tagged PNIPAm system with a ratiometric response to Cu(II) and Zn(II) concentrations for assessing metal toxicity in environmental samples. Towards that end, we have begun to carefully characterize the interactions of Cu(II), Zn(II), and other metal ions with a monodisperse PNIPAm homopolymer. The interactions of metal ions with pure PNIPAm is relatively unstudied despite decades of PNIPAm research. To more easily observe a metal’s influence on PNIPAm’s phase transition and aggregation, we have developed a light scattering strategy using a perpendicular detection fluorometer. By measuring Second Order Scattering intensities and applying a Mie theory interpretation we are able to monitor in situ particle aggregation on the 10 to hundreds of nanometer scale in a comparable manner to more expensive instrumentation. We found that when raised above the Lower Critical Solution Temperature linear NIPAm homopolymer (Mn = 8.4 and 10.3 kDa) aggregated to larger particles sizes when in the presence of Cu(II) and Zn(II). Binding interactions directly between PNIPAm and Cu(II) were confirmed using equilibrium dialysis. The observed size trends were rationalized as a function of metal ion concentration according to a metal crosslinking scheme.

Light scattering study on the interaction of poly(N-isopropylacrylamide) and transition metal dications

253rd National Meeting (2017)

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